Orthodontic brackets which are applied to teeth, either by attachment to a band or by direct bonding to a tooth, for the purpose of applying a moving force to the tooth to which the bracket is attached are known in the art. The moving force is generated by a wire attached to the orthodontic bracket which wire is also attached to similar brackets attached to adjoining teeth. The moving force applied to teeth over a period of time permits the movement of the teeth to accomplish desired alignment of the teeth.
There are basically two techniques for applying this moving force currently in practice in the orthodontic field. The conventional edgewise technique of applying this moving force is characterized by the use of a bracket having a rectangularly sectioned archwire receiving slot (edgewise slot). The moving force in this type of bracket (edgewise bracket) is applied to the tooth by the application of an angular torque from a mating edgewise archwire. The archwire is captured in the edgewise slot by a relatively small gauge stainless steel tie wire or by a small donut-shaped retaining member made from a resilient rubber-like material.
The edgewise bracket is typically used for bodily movement of teeth. To accomplish this movement more expeditiously, edgewise brackets are often designed to induce a predetermined type of force. These predetermined forces include, for example, a torque force to adjust a tooth with respect to its labio-lingual inclination or an angulation force to adjust the mesio-distal positioning of individual teeth. Brackets which have these predetermined forces built into their design are said to be pretorqued and preangulated. Pretorqued and preangulated edgewise brackets reduce the need for time and labor intensive archwire adjustments.
Another built-in design feature of prior art edgewise brackets is "in/out" compensation. This type of compensation is necessary due to variation in crown facial prominence; that is, the distance from the embrasure line to each crown's most prominent facial point. Average maxillary crown prominence ranges from approximately 2.9 mm for first and second maxillary molars to 1.65 mm for maxillary lateral incisors and from 2.5 for mandibular molars to 1.2 mm for mandibular incisors. When an archwire is applied to a series of edgewise brackets without in/out compensation, a smooth curve of the archwire will not meet all of the edgewise brackets. Therefore, a series of complicated bends must be made in the archwire in order to properly engage each edgewise slot. The bending of an archwire to fit the in/out of a particular patient's teeth requires a significant amount of time and effort. Accordingly, edgewise brackets have been made with built-in in/out compensation provided by edgewise brackets having various base thicknesses. The variable base thicknesses adjust the distance of the edgewise slot from the tooth surface and thereby place the edgewise slot of the edgewise bracket in alignment with adjacent edgewise brackets so that an archwire having a smooth curved shape can be attached to each bracket.
The other orthodontic technique which is presently used is known as the Begg lightwire technique. This technique involves the use of a relatively light, round sectioned archwire. A lighwire bracket typically includes a mesio-distally extending slot for receiving the archwire. The archwire is captured and secured in the lightwire slot by a pin having an elongate body portion and an enlarged head portion. The pin is inserted into a slot in the body of the lightwire bracket which thereby captures the archwire between the head of the pin and the body of the bracket. The pin is then secured to the lightwire bracket by bending the elongate portion of the pin over the body of the bracket. An example of a lightwire bracket is shown in U.S. Pat. No. 3,178,821.
The archwire slot of the lightwire bracket and the pin method of attaching an archwire thereto permits free tipping of the teeth (either labio-lingually or angularly). The lightwire brackets of the prior art have not been known to include pretorque, preangulation or proper in/out compensation.
Both the edgewise technique and the lightwire technique have advantages under different circumstances. Furthermore, both techniques may be used at different times on the same patient or in conjunction with each other at the same time on the same patient. Therefore, in addition to edgewise brackets and lightwire brackets, there have been developed combination brackets. Such combination brackets permit the use of either the edgewise technique or the lightwire technique using the same bracket. Examples of such combinations brackets are shown in U.S. Pat. Nos. 3,178,822 and 3,163,933. Although in/out compensation is provided in prior art combination brackets for the edgewise slot, in/out compensation has not heretofore been provided for both the edgewise slot and the lightwire slot.
Furthermore, because of the configuration of prior art orthodontic brackets, both an edgewise archwire and a lightwire archwire could not be attached to the bracket using a single fastening pin or a single fastening member. The use of multiple fastening members to attach both archwires is undesirable because they require additional labor to install those fastening members and they provide additional patient discomfort. Also, prior art combination brackets have heretofore been undesirably large causing difficulties in application and patient discomfort.
Therefore, a combination orthodontic bracket has long been sought which can be used for both edgewise and lightwire corrective techniques, which provides in/out compensation in both the edgewise slot and the lightwire slot, which requires only a single fastening member to attach both archwires to the bracket and which is relatively small and comfortable to wear.